Combination thread swaging and fastening screws



Oct. 26, 1965- s. S.'KAHN 3,213,742

COMBINATION THREAD SWAGING AND FASTENING SCREWS Filed July 18, 1963 2 Sheets-Sheet 2 INVENTOR. [60b l6e SIMON s. KA HN iw (Z Z. W 7 ATTYS.

United States Patent 3,213,742 COMBINATION THREAD SWAGING AND FASTENING SCREWS Simon S. Kahn, Glen Ridge, N.J., assignor to General American Transportation Corporation, Chicago, 11]., a corporation of New York Filed July 18, 1963, Ser. No. 296,003 7 Claims. (Cl. 85-46) The present invention relates to combination threadswaging and fastening screws, and more particularly to such screws adapted to swage threads of desired formation in generally cylindrical surfaces.

A general object of the invention is to provide a combination thread-swaging and fastening screw that comprises an elongated shank including a generally cylindrical rear body portion and a generally frusto-conical forwardly tapered front pilot end portion, a continuous thread carried on the shank and including both a plurality of helical turns on the rear body portion and a plurality of helical turns on the front pilot end portion, the thread having a fixed pitch, the turns on the rear body portion having substantially the same minor radius and successively forward ones of the turns on the front pilot end portion having gradually reduced minor radii, the turns on the rear body portion having a first crest projection from the root thereof and the turns on the front pilot end portion having a second crest projection from the root thereof, wherein the first crest projection is greater than the second crest projection, and a plurality of thread-swaging lobes carried by the turns on the front pilot end portion along the helix of the thread with a rotational angle A about the longitudinal axis of the shank between the centers of adjacent ones of the lobes, wherein A=360+B, and wherein B is a fixed angle within the approximate range 60 to 120, each of the lobes subtending a rotational angle C about the longitudinal axis of the shank, wherein C is a given angle within the approximate range 60 to 120, each of the lobes including a crest provided with leading and trailing edges and a pair of flanks each provided with leading and trailing faces, the leading and trailing edges of each lobe crest respectively merging into the adjacent portions of the crest of the associated turn on the front pilot end portion, and the leading and trailing faces of each lobe flank respectively merging into the adjacent portions of the flank of the associated turn on the front pilot end portion.

Another object of the invention is to provide a screw of the character described, wherein each of the lobes has a variable crest projection from the root thereof that is maximized substantially at the center thereof and that at its maximum value is substantially greater than the second crest projection of the associated turn on the front pilot end portion, and wherein the maximum crest projection of the rearmost of the lobes is substantially equal to the first crest projection of the turns on the rear body portion.

Another object of the invention is to provide a screw of the character described, wherein each of the lobes has a variable flank width at the root thereof that is maximized substantially at the center thereof and that at its maximum value is substantially greater than the flank width of the associated turn on the front pilot end portion, and wherein the maximum flank width of the rearmost of the lobes is substantially equal to the flank width of the turns on the rear body portion.

A further object of the invention is to provide a screw of the character described, that includes an enlarged toolengaging head on the rear end of the shank thereof, whereby the screw swages a thread in a preformed opening provided in an associated workpiece, as the screw is set in the workpiece.

Further features of the invention pertain to the particu'l'ar arrangement of the elements of the screw, whereby the above-outlined and additional operating features thereof are attained.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification, taken in connection with the accompanying drawings, in which:

FIGURE 1 is a side view of a blank that is employed in making the fluteless thread-forming screw embodying the present invention;

FIG. 2 is a side elevational view of the thread-swaging and fastening screw embodying the present invention;

FIG. 3 is an enlarged diagrammatic illustration of the profile of the front portion of the thread provided on the front pilot end of the shank of the screw shown in FIG. 2;

FIG. 4 is an enlarged diagrammatic illustration of the plan of the front portion of the thread, as shown in FIG. 3;

FIG. 5 is a greatly enlarged fragmentary side elevational view of the front portion of the screw, as shown in FIG. 2, and illustrating in proper positions certain of the swaging lobes incorporated in the front portion of the thread and developed in FIGS. 3 and 4; and

FIG. 6 is an enlarged diagrammatic illustration of the proper angular positions of certain of the swaging lobes mentioned.

Referring now to FIGS. 2 to 6, inclusive, of the drawings, there is illustrated a fluteless thread-forming tool, in the form of a combination thread-swaging and fastening screw 10, and embodying the features of the present invention; which screw 10 comprises an elongated shank 11 including a forwardly tapered substantially frustoconical front pilot end portion 11a and a substantially cylindrical rear body portion 11b. Also, the screw 10 comprises an enlarged head 12 terminating the extreme rear end of the rear body portion 11b of the shank 11; which head 12 may be of any suitable type, a hexagon head 12 being illustrated for the purpose of the present description. The head 12 is adapted to be received in a cooperating driving tool, such as a socket wrench, not shown, that is employed to set the screw 10 in an obvious manner. Further, the screw 10 comprises a continuous rolled thread 14 carried on the shank 11 and including a plurality of front helical turns 14a, 14b, 14c, 14d, 14e and 14 disposed on the front pilot end portion 11a and a plurality of rear helical turns 14w, 14x, 14y, etc., disposed on the rear body portion 11b. Thus, there are six turns on the front pilot end portion 11a; whereby the turns 14a, 14b, 14c, 14d, 14c and 14; are sometimes referred to hereinafter, respectively, as the first, second, third, fourth, fifth and sixth turns on the front pilot end portion 11a.

The thread 14 has a fixed pitch; the turns 14w, 14x, 14y, etc., on the rear body portion 11b have substantially the same fixed minor radius; and successively forward ones of the turns 14 Me, 14d, etc., on the front pilot end portion 11a have gradually reduced minor radii. The turns 14w, 14x, 14y, etc., on the rear body portion 11b have substantially the same fixed major radius, and consequently a corresponding first fixed crest projection from the root thereof; and successively forward ones of the turns 14 14c, 14d,'etc., on the front pilot end portion 11a have gradually reduced major radii and consequently a corresponding second fixed crest projection from the root thereof. In the arrangement, the first crest projection of the rear turns 14w, 14x, 14y, etc., is substantially greater than the second crest projection of the front turns 14 14c, 14d, etc.; all as clearly shown in FIGS. 2 and 5. Specifically, the radial distances between the two broken lines 1511 extending through the crests of the rear turns 14w, 14x, 14y, etc., and the respective root lines of the rear turns 14w, etc., are greater than the radial distances between the two broken lines 15a extending through the crests of the front turns 14a, 14b, 14c, etc., and the respective root lines of the front turns 14w, etc., as illustrated in FIG. 5. Each rear turn 14w, etc., includes a crest and a pair of flanks disposed with an angle of approximately 60 therebetween and with a first flank width at the root thereof; and each front turn 14a, etc., includes a crest and a pair of flanks disposed with an angle of approximately 60 therebetween and with a second flank Width at the root thereof. Of course, the flank width mentioned of each rear turn 14w, etc., is substantially greater than the flank width mentioned of each front turn 14a, etc.

Also, the screw comprises a plurality of threadswaging lobes 16a provided on the front turn 14a, 16c provided on the front turn 14c, 16d provided on the front thread 14d, and 16a provided on the front thread 14e; all as shown in FIGS. 3 and 4. Thus, the lobes are four in number and are carried by the turns on the front pilot end portion 11a along the helix of the thread 14 with a rotational angle A about the longitudinal axis of the shank 11 between the centers of adjacent ones of the lobes; wherein A==360+B; and wherein B is a fixed angle of approximately 120, as illustrated. Hence, in the present example A=480, as shown in FIGS. 3 and 4. Also, each of the lobes subtends a rotational angle C about the longitudinal axis of the shank 11; wherein C is a given angle of approximately 120, as illustrated. These relationships are shown in the developments of FIGS. 3 and 4; and also in FIG. 6, wherein it will he observed that the lobes 16a, 16c, 16d and 16e are respectively indicated in the clockwise direction. Further, this relationship is indicated in FIG. 5. Hence, in four complete turns of the thread 14 on the front pilot end portion 11a, or 1440 thereof, the lobe 16c falls directly behind and in alignment with the lobe 16a. The lobe 160 is angularly displaced by 480, or by an apparent angle of 120, with respect to the lobe 16a; the lobe 16d is angularly displaced by 480, or by an apparent angle of 120, with respect to the lobe 16c; and the lobe 16e is angularly displaced by 480", or by an apparent angle of 120, with respect to the lobe 16d.

As best illustrated in FIG. 5, the lobes 16a, 16c, 16d, and 16s are of substantially identical construction and arrangement, except the sizes of the lobes 16a, etc., progressively increase rearwardly along the front pilot end portion 11a. Thus, by way of example, and as best illustrated in FIG. 4, the lobe 16d provided on the front turn 14d comprise a crest 16d1 provided with leading and trailing edges 16d1L and 16d1T, and a pair of flanks 16d2 and 16d3 respectively provided with leading and trailing faces 16d2L, 16d2T and 16d3L, 16d3T. The leading and trailing edges 16d1L and 16d1T of the lobe crest 16d1 respectively merge into the adjacent portions of the associated front turn 14d; the leading and trailing faces 16d2L and 16d2T of the lobe flank 16d2 respectively merge into the adjacent portions of the corresponding flank of the associated front turn 14d; and the leading and trailing faces 16d3L and 16d3T of the lobe flank 16d3 respectively merge into the adjacent portions of the corresponding flank of the associated front turn 1411!. The leading crest edge 16d1L rises gradually radially out of the crest of the associated front turn 14d; and the trailing crest edge 16d1T falls gradually radially back into the crest of the associated front turn 14d. Hence, the lobe 16 has a variable crest projection from the root thereof that is maximized substantially at the center thereof and that at its maximum value is substantially greater than the second crest projection of the associated turn 14d. The l ading flank face 16d2L rises gradually both radially and axially forwardly out of the corresponding flank of the associated front turn 14d, and the trailing flank face 16d2L falls gradually both radially and axially rearwardly back into the corresponding flank of the associated front turn 14d; and similarly, the leading flank face 16d3L rises gradually both radially and axially rearwardly out of the corresponding flank of the associated front turn 14d, and the trailing flank face 16d3T falls gradually both radially and axially forwardly back into the corresponding flank of the associated front turn 14d. Hence, the lobe 16d has a variable flank width at the root thereof that is maximized substantially at the center thereof and that at its maximum value is substantially greater than the flank width of the associated front turn 14d.

The progressively increasing sizes of the lobes 16a, 16c, 16d and 16a rearwardly along the front pilot end portion 11a is best illustrated in FIG. 4, wherein it will be observed that the lower broken line 15c passing through the bottoms of the crest of the lobes 16a and 16c is disposed below the adjacent lower broken line 15a. Also, the upper broken line 15d, corresponding to the lower broken line 150, is disposed above the corresponding upper broken line 15a passing through the tops of the front turns 14a, etc., so as further to indicate that the maximum crest projections of the lobes 16a, etc., are substantially greater than the crest projection of the front turns 14a, etc. Thus, the maximum crest projection of the rearmost lobe 1642 is substantially equal to the crest projection of the rear turns 14w, 14x, etc.; and similarly, the maximum flank width 16e is substantially equal to the flank width of the rear turns 14w, 14x, etc.

Reconsidering the rotational angle A between the centers of the adjacent ones of the lobes 16a, 16c, 16d and 16a, this angle A=360+B, but B may be in the general range 60 to 120; whereby with a smaller angle B, the number of lobes on the turns carried on the front pilot end portion 11a is increased, assuming that there are six such turns thereon, as described above. Also, the provision of six such turns on the front pilot end portion 11a is not critical, and such number may be correspondingly increased by lengthening the front pilot end portion 11a, assuming a fixed pitch of the thread 14, as described above. Of course, a shorter pitch of the thread 14 will produce an increased number of turns on the front pilot end portion 11a, assuming a given length thereof.

Now in this formula, the angle B may have any desired value in the approximate range 60 to 120. When the angle B has a value (30, 36, 40, 45 or 60) that is evenly divisible into 360, the lobes in the thread 14 are disposed in straight rows extending longitudinally along the front shank portion 11a; and when the angle B has a value that is not evenly divisible into 360, the lobes in the thread 14 are disposed in skewed rows extending longitudinally along the front shank portion 11a. In these several embodiments of the thread 14: when the angle B is 60", there are 6 longitudinally extending rows of lobes; when the angle B is 72, there are 5 longitudinally extending rows of lobes; when the angle B is there are 9 longitudinally extending rows of lobes; when the angle B is there are 4 longitudinally extending rows of lobes; and when the angle B is there are 3 longitudinally extending rows of lobes. In each case, the rows of lobes are equally spaced-apart about the longitudinal center line of the shank 11. While a wide wariety of these thread formations are entirely satisfactory, it has been found that these designs involving an odd number of rows of lobes are generally preferred, since these thread formations are easier to drive and provide a better balance of the torque required in the starting of the front pilot end portion of the thread 14 into the pilot hole provided in the associated workpiece, not shown.

Reconsidering the rotational angle C that is subtended by each of the lobes 16a, 16c, 16d and 16e, the illustrated example of 120 is not critical, although this angle C should be substantial; whereby C may be in the general range 60 to 120.

The preferred embodiment of the screw illustrated, wherein both the angle B=120 and the angle C: 120, is very advantageous, since the same is characterized by an exceedingly small torque, as compared to other of the embodiments mentioned, required to effect rotation of the screw 10 to cause setting thereof in a standard preformed pilot hole provided in a standard workpiece used herein in testing various thread formations of the screws 10, embodying the present invention and of the construction and arrangement described above. It is believed that this result is produced by the cooperation between the dimensional and positional arrangements of the elements of the thread 14 in the preferred embodiment of the screw 10, as previously described.

Turning now to the present method of making the screw 10, a corresponding blank B10 is provided, as illustrated in FIG. 1. The blank B10 is forged or formed of metal and comprises an elongated shank B11 including a substantially frusto-conical front pilot end portion Ella and a substantially cylindrical rear body portion 1311b. Also, the blank B10 comprises the hexagon head B12 terminating the rear end of the rear body portion B111). Also, there are provided a pair of rolling dies, not shown, of flat plate-like construction. The shank 11B of the blank B10 is subjected to rolling pressure between the complementary and mating dies, whereby the flutes and lands disposed in the rolling dies mentioned produce the continuous thread 14 in the shank 11 of the screw 10; all in a well-known manner.

Ordinarily, the metal blank B10 is formed of low carbon steel; and after the screw 10 is formed therefrom in the present rolling method, the same is subjected to heat treatment so as to case harden it, in a Well-known manner. Specifically, it is highly desirable that the front helical turns 14w, etc., be quite hard, since the screw 10 is frequently employed in forming an internal thread in a cylindrical hole provided in a workpiece, when such workpiece is formed of steel, or other hard material.

In view of the foregoing, it is apparent that there has been provided a fluteless thread-forming tool, and specifically a fastening screw of improved construction and arrangement. This tool is very advantageous, since the same is operative to form the internal thread in the generally cylindrical surface of a pilot hole formed in a workpiece altogether by a swaging action, and without the formation of chips or cuttings from the workpiece. Moreover, the improved tool is substantially easier to operate in its thread-forming action than is a comparable conventional tool of the chip-forming type, in the sense that the improved tool requires substantially less driving torque than does the conventional tool mentioned.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A combination thread-swaging and fastening screw comprising an elongated shank including a generally cylindrical rear body portion and a generally frusto-conical forwardly tapered front pilot end portion, a continuous thread carried on said shank and including both a plurality of helical turns on said rear body portion and a plurality of helical turns on said front pilot end portion, said thread having a fixed pitch, the turns on said rear body portion having substantially the same minor radius and successively forward ones of the turns on said front pilot end portion having gradually reduced minor radii, the

turns on said rear body portion having a first fixed crest projection from the root thereof and the turns on said front pilot end portion having a second fixed crest projection from the root thereof, wherein said first fixed crest projection is greater than said second fixed crest projection, and a plurality of separate and distinct thread-swaging lobes carried entirely by the turns on said front pilot end portion along the helix of said thread with a rotational angle A about the longitudinal axis of said shank between the centers of adjacent ones of said lobes, where A'='360+B and wherein B is a fixed angle within the approximate range 60 to 120, each of said lobes subtending a rotational angle C about the longitudinal axis of said shank, wherein C is a given angle within the approxi mate range 60 to 120, each of said lobes including a crest provided with leading and trailing faces, the leading and trailing edges of each of said lobe crests respectively merging into the adjacent portions of the crest of the associated turn on said front pilot end portion, the leading and trailing faces of each of said lobe flanks respectively merging into the adjacent portions of the flank of the associated turn on said front pilot end portion, each of said lobes having a variable crest projection from the root thereof that is maximized substantially at the center thereof and that at its maximum value is substantially greater than said second fixed crest projection of the associated turn on said front pilot end portion and each of said lobes having a variable flank width at the root thereof that is maximized substantially at the center thereof and that at its maximum value is substantially greater than the flank width of the associated turn on said front pilot end portion, the maximum crest projection of the rearmost of said lobes on said front pilot end portion being substantially equal to said first fixed crest projection of the turns on said rear body portion and the maximum flank width of the rearmost of said lobes on said front plot end portion being substantially equal to the flank width of the turns on said rear body portion.

2. The screw set forth in claim 1, wherein B is approximately 120.

3. The screw set forth in claim 1, wherein C is approximately 120.

4. The screw set forth in claim 1, wherein B and C are approximately equal.

5. The screw set forth in claim 1, wherein B is approximately 120" and C is approximately 120.

6. The screw set forth in claim 1, wherein the leading edge of the crest of each of said lobes rises gradually radially out of the adjacent portion of the crest of the associated turn on said front pilot end portion and the trailing edge of the crest of each of said lobes falls gradually radially back into the adjacent portion of the crest of the associated turn on said front pilot end portion.

7. The screw set forth in claim 1, wherein the leading face of each flank of each of said lobes rises gradually both radially and axially out of the adjacent portion of the flank of the associated turn on said front pilot end portion and the trailing face of each flank of each of said lobes falls back gradually both radially and axially into the adjacent portion of the flank of the associated turn on said front pilot end portion.

References Cited by the Examiner UNITED STATES PATENTS 66,766 7/67 Young 47 2,167,559 7/39 Upson 8546 2,352,982 7/ 44 Tomalis 8546 2,991,491 7/ 61 Welles.

FOREIGN PATENTS 1,265,999 5/ 61 France.

CARL W. TOMLIN, Primary Examiner.

EDWARD C. ALLEN, Examiner. 

1. A COMBINATION THREAD-SWAGING AND FSTENING SCREW COMPRISING AN ELONGATED SHANK INCLUDING A GENERALLY CYLINDRICAL REAR BODY PORTION AND A GENERALLY FRUSTO-CONICAL FORWARDLY TAPERED FRONT PILOT END PORTION, A CONFINUOUS THREAD CARRIED ON SAID SHANK AND INCLUDING BOTH A PLURALITY OF HELICAL TURNS ON SAID REAR BODY PORTION AND A PLURALITY OF HELICAL TURNS ON SAID FRONT PILOT END PORTION, SAID THREAD HAVING A FIXED PITCH, THE TURNS ON SAID REAR BODY PORTION HAVING SUBSTANTIALLY THE SAME MINOR RADIUS AND SUCCESSIVELY FORWARD ONES OF THE TURNS ON SAID FRONT PILOT END PORTION HAVING GRADUALLY REDUCED MINOR RADII, THE TURNS ON SAID REAR BODY PORTION HAVING A FIRST FIXED CREST PROJECTION FROM THE ROOT THEREOF AND THE TURNS ON SAID FRONT PILOT END PORTION HAVING A SECOND FIXED CREST PROJECTION FROM THE ROOT THEREOF, WHEREIN SAID FIRST FIXED CREST PROJECTION IS GREATER THAN SAID SECOND FIXED CREST PROJECTION, AND A PLURALITY OF SEPARATE AND DISTINCT THREAD-SWAGING LOBES CARRIED ENTIRELY BY THE TURNS ON SAID FRONT PILOT END PORTION ALONG THE HELIX OF SAID THREAD WITH A ROTATIONAL ANGLE A ABOUT THE LONGITUDINAL AXIS OF SAID SHANK BETWEEN THE CENTERS OF ADJACENT ONES OF SAID LOBES, WHERE A=360* + B AND WHEREIN B IS A FIXED ANGLE WITHIN THE APPROXIMATE RANGE 60* TO 120*, EACH OF SAID LOBES SUBTENDING A ROTATIONAL ANGLE C ABOUT THE LONGITUDINAL AXIS OF SAID SHANK, WHEREIN C IS A GIVEN ANGLE WITHIN THE APPROXIMATE RANGE 60* TO 120*, EACH OF SAID LOBES INCLUDING A CREST PROVIDED WITH LEADING AND TRAILING FACES, THE LEADING AND TRAILING EDGES OF EACH OF SAID LOBE CREST RESPECTIVELY MERGING INTO THE ADJACENT PORTIONS OF THE CREST OF THE ASSOCIATED TURN ON SAID FRONT PILOT END PORTION, THE LEADING AND TRAILING FACES OF EACH OF SAID LOBE FLANKS RESPECTIVELY MERGING INTO THE ADJACENT PORTIONS OF THE FLANK OF THE ASSOCIATED TURN ON SAID FRONT PILOT END PORTION, EACH OF SAID LOBES HAVING A VARIABLE CREST PROJECTION FROM THE ROOT THEREOF THAT IS MAXIMUM WUBSTANTIALLY AT THE CENTER THEREOF THAT AT ITS MAXIMUM VALUE IS SUBSTANTIALLY GREATER THAN SAIS SECOND FIXED CREST PRJECTION OF THE ASSOCIATED TURN ON SAID FRONT PILOT END PORTION AND EACH OF SAID LOBES HAVING A VARIABLE FLANK WIDTH AT THE ROOT THEREOF THAT IS MAXIMIZED SUBSTANTIALLY AT THE CENTER THEREOF AND THAT AT ITS MAXIMUM VALUE IS SUBSTANTIALLY GREATER THAN THE FLANK WIDTH OF THE ASSOCIATED TURN ON SAID FRONT PILOT END PORTION, THE MAXIMUM CREST PROJECTION OF THE REARMOST OF SAID LOBES ON SAID FRONT PILOT END PORTION BEING SUBSTANTIALLY EQUAL TO SAID FRIST FIXED CREST PRJECTTION OF THE TURNS ON SAID REAR BODY PORION AND THE MAXIMUM FLANK WIDTH OF THE REARMOST OF SAID LOBES ON SAID FRONT PLOT END PORTION BEING SUBSTANTIALLY EQUAL TO THE FLANK WIDTH OF THE TURNS ON SAID REAR BODY PORTION. 